1. Field of the Invention
The present invention relates generally to a semiconductor technique and more particularly to a method for forming an interlayer insulation film having a low dielectric constant (low-k) on a semiconductor substrate by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of the Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique attracts a great deal of attention. These multi-layered structures, however, capacitance among individual wires hinders high-speed operations. In order to reduce the capacitance it is necessary to reduce the dielectric constant (relative permittivity) of the insulation film. Thus, various materials having a relatively low dielectric constant have been developed for insulation films.
As shown in the table below, along with reduction of a device node, a low dielectric constant value (Low-k) is required for an interlayer insulation film used for the device concerned.
As to Low-k films with a dielectric constant of approximately 2.7, because many deposition methods such as a CVD method, coating method, etc. have been proposed, high-quality Low-k deposition becomes possible in recent years. As a result, application of the films to mass-produced devices with a device node of 0.10 to 0.13 xcexcm has just started. For next-generation high-speed devices, Low-k films having a furthermore lower dielectric constant of approximately k=2.5 or less will be required. Additionally, to manufacture devices, improving reliability of the devices is attempted by incorporating a hard layer being relatively hard with a high dielectric constant on the top, intermediate or the bottom surface of the Low-k film. Because a dielectric constant increases if the hard layer is incorporated in this way, Low-k films with a low dielectric constant as much as possible are required.
The present invention enables forming a low dielectric constant film of k less than 2.40 by introducing a pulse control flow of oxidizing gas into a gas containing silicon gas using a CVD method. Further, although conventional methods for controlling oxygen are different from the present invention, the present invention can be applied to conventional apparatus and make it possible to reduce capital investment manufacturing costs because CVD Low-k deposition devices for approximately k=2.7 deposition can easily be modified and used for the present invention. In the present invention, oxidizing gas is introduced in pulses and is mixed with and made to react with a source gas (material gas for forming a film) comprising silicon in a reaction zone. By pulse-controlling the flow of oxidizing gas in plasma CVD processing, the reactivity of the reaction gas (composed of the source gas and the oxidizing gas) can effectively be controlled, forming a low dielectric constant film. The residence time of the reaction gas in the reaction zone or the type of silicon-containing gas such as Sixcex1Oxcex1xe2x88x921R2xcex1xe2x88x92xcex2+1(OCHnH2n+1)xcex2 gas is not prerequisites for practicing the present invention. However, these factors may be controlled, and in embodiments, DM-DMOS (Dimethydimetoxysilane, Si(CH3)2(OCH3)2) and oxygen may be used, oxygen may be used as an oxidizing agent, and a low-dielectric film may be formed, as disclosed in U.S. patent application Ser. No. 09/827,616, filed Apr. 6, 2002. The disclosure of the application is herein incorporated by reference in its entirety.
In an embodiment, the present invention provides a method for forming an insulation film on a semiconductor substrate, comprising the steps of: (i) introducing a source gas comprising a compound composed of at least Si, C, and H into a chamber; (ii) introducing in pulses an oxidizing gas into the chamber, wherein the source gas and the oxidizing gas form a reaction gas; and (iii) forming an insulation film on a semiconductor substrate by plasma treatment of the reaction gas. In the above, the plasma treatment may be plasma CVD processing. The plasma CVD processing includes plasma-enhanced CVD (PECVD) processing and remote plasma processing in which the reaction zone and the film formation zone are different. Any suitable CVD processing can be employed.
Increasing a flow of oxidizing gas increases the reactivity of the reaction zone and the size of fragments formed in the reaction zone, which lowers the dielectric constant value because a film obtained includes vacancies or pores between fragments accumulated. It is inferred that when an oxidizing gas flow increases, the size of fragments forming in the reaction zone increases, a vacancy rate or porosity of the film increases and a dielectric constant decreases. However, lowering a k value up to approximately 2.45 appears to be the limit even if the flow of oxidizing gas increases. If the oxygen amount increases more, dust is generated in the reaction zone and high-quality films cannot be obtained, and these films may not possess any measurable dielectric constant. Additionally, plasma becomes unstable and a stable reaction cannot be maintained. In the present invention, by introducing an oxidizing gas in pulses, surprisingly, the above problems can be eliminated.
In an embodiment, the compound is an organo silicon of SixCyOzHa wherein a, x, y, and z are integers. The source gas comprises silicon-containing gas and optionally inert gas such as H and Ar (e.g., less than a half of the silicon-containing gas). The oxidizing gas may be included in an additive gas which may further include inert gas or reducing gas, depending on the reaction of film formation.
The oxidizing gas may be introduced in the chamber in cycles of 5 msec to 10 sec, although the duration of one cycle can be shorter or longer than the above, including 1 msec and 20 sec depending on the reaction of film formation. A pulse cycle is repeated multiple times, e.g., 2-10,000 times including 10, 100, 1,000 times, during the film formation process. In an embodiment, the oxidizing gas is introduced in the chamber in cycles of 100 msec to 5 sec. The oxidizing gas can be oxygen, N2O, or any other gas which can function as an oxidizing agent, including CO2, H2O; a cyclic organic compound having the formula (CH2O)n such as 1,3,5-trioxan; or an alkanol compound having the formula CxH2x+1OH (x is an integer) such as ethanol, methanol, n-propanol, or 1-propanol. In the above, alkanol itself is considered to be a reducing agent, but when alkanol is mixed with an organo silicon gas for film formation, a source gas oxidization reaction occurs. Thus, alkanol functions as an oxidizing agent. The usable oxidizing agent is not limited to the above and any of the foregoing can be used singly or in any combination.
In an embodiment, the introduction of the oxidizing gas in pulses can be achieved by introducing alternately (i) a first reaction gas comprising the source gas at a base flow rate and the oxidizing gas at a flow rate of 50% or higher of the base flow rate, and (ii) a second reaction gas comprising the source gas at a base flow rate and no oxidizing gas or the oxidizing gas at a flow rate of 50% or less of the base flow rate. The total flow of the oxidizing gas may be less than the flow of the source gas or in an embodiment, less than 50% of the source gas.
In the present invention, the pulses and the flow of the oxidizing gas can be selected so as to adjust a dielectric constant of the insulation film to 2.45 or less.
A plasma may be formed by RF power, although microwave power can be used in an embodiment. Further, when RF power is used, the intensity of RF power may be pulsed in cycles synchronized with the pulsed flow of the oxidizing gas, so that low-dielectric films can effectively be formed. In an embodiment, the intensity of RF power is higher in cycles when the oxidizing gas flow is low than in cycles when the oxidizing gas flow is high. In an embodiment, the intensity of RF power may be pulsed in cycles of 1 msec or more, independently of the pulses of the oxidizing gas flow.
Additionally, the formation of the insulation film may be conducted while maintaining a temperature of a shower plate at 150xc2x0 C. or higher, through which the reaction gas passes into the chamber.
The insulation film may be a cap layer having a thickness of 10 nm or more in an embodiment, although the type or usage of film should not be limited.
The present invention enables forming of a low dielectric constant film in the plasma CVD method. By using this low dielectric constant film as an insulation film for next-generation highly integrated semiconductor elements, delay caused by wiring capacity can be lowered and the operation speed of a semiconductor element can be substantially increased.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.